In providing telephony services it is often desirable to detect particular calling activity with respect to one or more parties to a call. For example, a local exchange carrier (LEC) may employ logic at a central office (CO) switch for detecting a subscriber's desire to invoke enhanced calling services. A subscriber may signal a CO switch of the LEC providing his telephony service that connection to a second line, as provided by a call waiting enhanced service, is desired by instigating a hook flash (releasing and reconnecting the line within a predetermined window of time). Similarly, a subscriber may signal a CO switch of the LEC providing his telephony service that conferencing of multiple lines, as provided by a three-way calling enhanced service, is desired by instigating a hook flash. Each of the foregoing examples sets forth a situation in which the subscriber is providing signaling which the subscriber desires to be detected by the appropriate CO equipment without reason to try and mask or hide the signaling from other telephony equipment.
However, in some situations particular call activity may be unauthorized, impermissible, or otherwise undesired. For example, in a prison setting it may be desirable to prevent a prisoner from calling particular parties, such as victims, judges, prosecuting attorneys, and the like, although such prisoners may be granted the privilege of calling friends and families. Although it may be relatively straight forward to implement logic in a prison phone system to prevent a prisoner from directly calling particular identified numbers or allowing a prisoner to call only particular identified numbers, the possibility of a miscreant accomplice may result in a prisoner being able to complete an unauthorized call. For example, an individual to which a prisoner is allowed the privilege of placing calls may invoke enhanced calling services, such as three-way calling, through his LEC to thereby place a calling prisoner in contact with a number which the prisoner is otherwise not permitted to call.
It should be appreciated that, although the accomplice may purposefully signal a CO associated with the LEC providing his telephony service in order to implement the aforementioned three-way calling service, the prison telephony system or other calling party side equipment associated with the prisoner's end of the call is not purposefully signaled. Accordingly, it is often exceedingly difficult to detect and/or prevent such calling activity. Moreover, the individuals engaged in such activity generally recognize that it is forbidden and go to great lengths to attempt to thwart techniques for detecting and preventing unauthorized calling activity.
Several attempts have been made in the art to detect and/or prevent three-way calling. For example, U.S. Pat. No. 5,319,702 issued to Kitchin utilizes analysis of hook flash wave forms to detect three-way calling. However, such wave forms are not always sufficiently predictable when passed through various networks and switches, e.g., local verses long distance calls and digital verses analog switches can result in such waveforms being appreciably different from call to call. U.S. Pat. No. 5,926,533 issued to Gainsburo implements tone detection to detect three-way calling. However, detection of such tones may be avoided by a party instigating the three-way calling properly timing their hook flash signaling. Moreover, such tones may be masked to avoid detection through introduction of masking signals, e.g., continuous loud noise, into the call during the tones. Accordingly, the foregoing techniques for detecting and/or preventing three-way calling often do not accurately recognize the three-way calling activity.